This invention relates to battery charging device and, more particularly, to an electromagnetic induction, non-contact type battery charging device suited for charging batteries of a self-propelled apparatus such as electric vehicles.
In conventional battery charging devices, there are two types of charging systems, namely, conductive charging device and an inductive charging device. The inductive charging device is also called an electromagnetic, non-contact type battery charging device. The inductive charging device is advantageous in that it cannot be hindered by a bad electrical contact unlike the conductive charging device. Further, with the use of the inductive charging device, vehicles are not required to carry large battery charging equipment, and the size of the battery charging device can be reduced.
Charging of the battery is usually achieved by inserting a power supply coupler connected to a power supply device with a cable into a power receiver coupler mounted within the electric vehicle. When the couplers are coupled to one another, the couplers transmit or receive information necessary for setting charging conditions by means of respective internal communication units.
In the prior art battery charging device discussed above, the charging of the battery is done at high frequency and at high rates, there is a great deal of heat buildup in the power supply charging coupler. In order to prevent the power supply coupler from being damaged due to thermal shock, it is a usual practice to have the power receiver coupler equipped with a cooling unit of an air type or a water type. The power receiver coupler is also equipped with a temperature sensor, which serves to monitor the operating temperature of the power receiver coupler during charging and to transmit a temperature signal related to the detected temperature to a control unit of the power supply device via the communication unit of the power supply coupler. When the battery charger overheats, the control unit of the power supply device serves to stop the charging of the battery in response to the temperature signal delivered from the temperature sensor.
However, even when such thermal protection is carried out, if there is a failure in the communication system, it is difficult to prevent a decrease in cooling performance or an abnormal operating condition of the power supply coupler.
In the prior art battery charging device as discussed above, the cooling performance and overheating is usually detected by a detector incorporated in the power receiver coupler. For this reason, if the temperature of the power supply coupler is excessive and the temperature of the power receiver coupler is not excessive, charging of the battery continues. As the charging of the battery continues, the temperature of the power supply coupler further increases, which may cause unstable operation of the communication units and cause difficulties in achieving a stable charging of the battery. In addition, the power supply coupler is subject to thermal distortion and various component parts incorporated in the power supply coupler are subject to thermal cracking.